1. Field of the Invention
Embodiments of the present invention relate to integrated circuits. More specifically, certain embodiments relate to methods and apparatuses for efficiently distributing power in an integrated circuit.
2. Background
The power distribution network of an integrated circuit (“IC” or “chip”) distributes power (voltage and ground) to the devices in the chip. A robust power distribution network is essential to ensure reliable operation of chip components. As chips increase in complexity, voltage drop (“IR drop”) to chip components is becoming a larger problem. Shrinking device dimensions, increased number of devices, faster switching frequencies, and increased power consumption in deep sub-micrometer technologies are causing increased currents relative to conductor size, and thus IR drop. Thus, the voltage (and ground) delivered to chip components may be less than optimal. Increased IR drop causes several practical problems. For example, IR drops in the power grid reduce the maximum switching speeds and therefore limit reliable chip performance. Increased IR drop also decreases the noise margins of circuits, further limiting performance. As a result, a ten percent IR drop may reduce chip performance by seven to nine percent. If the IR drop becomes too large, critical timing paths in the chip will fail depending on manufacturing variances. Further, high average current densities may lead to electro-migration in the conductors, causing premature failure of the conductor. If these effects are not addressed, the IR drop decreases the reliability of manufactured chips—i.e., if IR drop exceeds expected values on individual chips, chip yields will be decreased or functional failures may occur in the field.
A straightforward method to decrease the IR drop to each chip component is to increase the size of the die's power grid. This is often achieved by increasing the number of metal layers delivering power (voltage and ground) to chip components. Increasing the number of metal layers, however, increases the cost per chip. When a manufacturer expects to sell tens or hundreds of millions of chips, a savings of even a few pennies per chip becomes significant. Therefore, what is needed is a more robust power distribution network. What is further needed is a robust power distribution network which reduces the number of metal layers in a chip.